Big-headed ant

The big-headed or coastal brown ant has spread worldwide and caused a lot of damage in new areas.

The big-headed ant is light yellow or ginger to a dark reddish brown. 

The worker ants come in two sizes. 

The smaller worker is 2mm to 3mm long, while the larger workers are 3mm to 4mm and have big heads that are out of proportion with their bodies.

In the Top End, big-headed ants prefer cooler temperatures with higher humidity. They are commonly found in urban areas, including Darwin, Katherine and Alice Springs.

Impact

Big-headed ants are aggressive and will kill native insects. By reducing insect numbers they compete with other native species that eat those insects.

They are badly affecting ant diversity through direct predation and by competing with them for food sources.

Reducing native ant numbers can have a major impact on the ecological balance. 

Native ants provide aeration and the addition of nutrients to the soil, pollination, spreading seeds and pest control.

In the Top End, big-headed ants threaten rainforests. 

At Howard Springs Nature Park the big-headed ant has eliminated 40 native ant species and reduced numbers of insects, snails, spiders and centipedes by around 85%.

Big-headed ants invade houses and can damage electrical wiring and the grouting between tiles and pavers.

In the Top End, their nest entrances are usually at the base of trees and shrubs. 

Their nests disturb root systems, dry out the soil and can lead to the death of trees and shrubs. 

When nests are in brick paving they can cause soil disturbance that can destabilise pathways.

Management

The best way to stop the spread of ants is to check items before moving them away from your home.

Amdro ant bait

Nests can be treated with the ant bait Amdro. 

Wide spreading or broadcasting of ant bait has been the best way to remove ant nests in gardens, around buildings, in plant nurseries and in non-crop farmland.

You must consider all of the following before using Amdro:

  • don't heap ant bait on the ant nest - this risks non-target animals and insects taking bait
  • when used as directed on packaging, this bait is not harmful for pets, livestock or children, but keep the bait out of reach of these when not in use
  • don't use ant bait inside bird cages, near water or in areas where it can be washed into waterways
  • don't use bait on wet ground or in the Wet Season
  • turn off sprinklers a day before using bait and don't use for a day after
  • you should use bait in the late afternoon or at night to avoid direct sunlight
  • treatment may take four to six weeks before the ants are gone
  • you will need to use bait every two to three months until ants are gone.

Coopex Residual Insecticide

Coopex Residual Insecticide is a safe pesticide to use inside homes or on areas around the home that are protected from water. 

You will need to use this pesticide every 12 weeks or until the ants are gone.

Don't disturb ants before using insecticide or pesticide. If you do the colony will likely move the queen to safety.

Pest control companies can also treat nests. You should try and treat ants with neighbours to stop ants returning.

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Last updated: 27 June 2017